Did 3I-carus fly too close to the Sun?
Interstellar comet 3I/ATLAS is losing an insane amount of mass after making its closest pass of the Sun last month — a phenomenon known as perihelion — prompting Harvard scientist Avi Loeb to speculate that the object might’ve fragmented into over a dozen pieces.
“Think of it as fireworks, resulting from the warming by the sunlight,” the astrophysicist told The Post in a Monday evening call. “The object exploded into multiple pieces.”
Interstellar comet 3I/ATLAS is losing an insane amount of mass after making its closest pass of the Sun last month, or perihelion, prompting Harvard scientist Avi Loeb to speculate that the object might’ve fragmented into over a dozen pieces. M. Jager, G. Rhemann, E. Prosperi
China’s Tianwen-1 orbiter sent back intriguing photos of interstellar comet 3I/ATLAS (pictured) taken from the orbit of Mars. CNSA
This dramatic weight loss would seem to point to the object’s cometary makeup — but Loeb is not willing to rule out extraterrestrial origins just yet.
The astrophysicist, who detailed his theory in a new post on Medium, based his fragmentation explanation on new images taken by British astronomers Michael Buechner and Frank Niebling, which show that ATLAS sprouted a massive “anti-tail” and a separate, “smoking” trail.
These mammoth jets extend an incredible distance of 620,000 miles towards the Sun and 1,860,000 miles in the opposite direction, respectively, indicating a massive mass loss amid the sunbeams, Loeb noted in his blog post.
“For a natural comet, the outflow velocity of the jets is expected to be [0.248 miles] per second… at the distance of 3I/ATLAS from the Sun,” he added. “At that speed, the jets must have persisted over a timescale (period) of 1–3 months.”
“The object exploded into multiple pieces,” Loeb (pictured) told The Post. Chris Michel/National Academy of Sciences
Loeb calculated that the cosmic visitor would’ve needed to absorb a ludicrous amount of energy from the Sun in order to sublimate (when a solid object changes from solid to gas) the large amounts of carbon dioxide ice and water ice required to shed such an insane amount of mass.
Based on ATLAS’ distance to the sun during perihelion, Loeb calculated that the absorbing area would’ve been around [617 square miles]” — equivalent to a sphere that’s 14.3 miles across.
That’s four times larger than the previous projection of a 3.1-mile diameter, with a mass of 33 billion tons, per Loeb.
“That’s much bigger than we expect for the size of the object based on the data we had from the Hubble telescope back on July 21st,” Loeb told The Post. “So that means that maybe if it’s a natural comet, it had to break up into a lot of fragments, a lot of pieces, at least tens of them, in order to increase the surface area to the value that you need.”
He added, “That’s what is needed in order to explain the amount of mass carried by the jets.”
An image of a new object C/2025 V1, taken on November 3, 2025. A. Ivanov et al.
This isn’t the only potential evidence that points to the object’s alleged cometary identity. On October 24, the MeerKAT radio telescope in South Africa picked up the first-ever radio signal from 3I/Atlas, Futurism reported.
The telescope, which failed to detect anything on two prior attempts in September, reportedly detected “radio absorption lines by hydroxyl radicals,” which are created when water molecules are broken down by sunlight.
This suggests that ATLAS is a comet that’s losing water when flying by the sun and not a potentially “hostile” alien probe sent to do recon on our solar system, as Loeb has suggested previously.
Nonetheless, these discoveries haven’t thrown water on Loeb’s theories that ATLAS could have extraterrestrial origins. He believes that if upcoming observations show that the interstellar visitor remained fairly intact during its tour of the sun, this could point to alien provenance, as a regular comet would’ve disintegrated.
An alternative explanation, per Loeb, is that the jets are engines of sorts.
“Technological thrusters require a much smaller mass loss in order to produce the observed jets around 3I/ATLAS,” he wrote in his recent blog. “Chemical rockets are propelled by an exhaust speed of [1.86 to 3.1 miles per second], which is ten times larger than the maximum ejection speed of volatiles (gases) sublimated by sunlight from natural cometary surfaces.”
He told The Post that “an alien technology can use even better thrusters than we currently employ.”
According to the scientist, these extraterrestrial rocket boosters would boast higher exhaust speeds, which would mitigate the required mass loss substantially while the fuel would comprise a “small fraction of the total mass of the of the spacecraft.”
“In that case, nothing would explode,” he said. “It would maintain its integrity.”
To truly determine whether ATLAS is natural or “technological,” the scientist said they would have to analyze the images of the comet’s twin jets when ATLAS makes its nearest pass of our planet next month.
“On December 19, 2025, 3I/ATLAS will get closest to Earth, allowing ground-based telescopes as well as the Hubble and Webb space telescopes to diagnose its integrity,” Loeb wrote in his post.
Coincidentally, this comes after photographs taken by an observatory in Spain on Nov. 5 showed no sign of a debris tail, which was expected to be trailing the object as it encountered the force of the sun.
This eliminated the conventional explanation for the surprising “non-gravitational acceleration” it exhibited last week, thereby fueling Loeb’s theory that ATLAS could be artificial.